In fabrication of a semiconductor wafer, an electrical or optical component or a printed circuit board, a workpiece will be subjected to one or more cleaning and drying processes in which, ideally, all foreign substances that are not intended to be incorporated in the workpiece are removed. Chemical baths containing strong acids, strong bases or oxidizers, such as HCl, H.sub.2 SO.sub.4, HNO.sub.3, H.sub.2 PO.sub.3, HF, NH.sub.4 OH and H.sub.2 O.sub.2, are often used as part of a cleaning process. These substances are often toxic, chemically reactive, corrosive and/or bioaccumulative and must be handled and disposed of as hazardous substances.
Several workers have disclosed methods for drying parts, including integrated circuits, by use of heated or superheated gases. One attractive method uses a drying vapor of heated isopropanol (IPA), which forms a minimum boiling azeotrope with water and is believed to displace water from the wafer surfaces, and the vapor flows into the vessel at one end and simultaneously flows out of the vessel at another end.
Other workers have disclosed use of a plurality of megasonic beam transducers, located at staggered positions, for cleaning wafers. Each transducer emits a vibratory megasonic beam with an unspecified (very high) frequency in a fixed direction, and the transducer locations are chosen so that the collection of beams irradiate, and thereby clean, all wafer surfaces in a chamber, no matter how the wafers are arranged.
Use of ultrasonic transducers in a chemical cleaning bath to cooperatively remove contaminants and unwanted material layers from semiconductor wafers, medical instruments and other objects of interest is disclosed by other workers. Still other workers have disclosed use of ultrasonic transducers to coat, spray, deposit or otherwise apply a desired material to an object surface, or for ultrasonic fogging.
These approaches use heated or superheated gases or direct beam irradiation to dry or clean an object surface; or they use cooperative action by an ultrasonic beam and an active chemical bath to remove contaminants from, or to apply a desired material to, an object surface. These approaches are complex, usually require operation at high temperatures, often require processing times of one to several minutes, and often require use of specially resistant chamber walls for the processing chamber. The chemicals used are often designated as hazardous substances, requiring special handling.
What is needed is a system that uses non-hazardous substances for chemically cleaning and/or drying workpieces and that is reasonably effective for removing substantially all foreign substances with diameters above a range of sizes, such as 0.1-0.5 .mu.m. Preferably, the system should also be effective for removing liquids from and drying and cleaning workpieces in relatively short time intervals. Preferably, the chemicals used should be recyclable and the energy requirements for the cleaning or drying process should be modest.